The present invention relates to a pneumatic tire, more particularly an improvement in a tread pattern, in which wet performance and low noise performance are both improved.
In general, a tire tread portion is provided with grooves for water drainage. However, such tread grooves especially lateral grooves make noise during running.
In order to reduce such a noise, the so called "variable pitching method" has been widely used. In such method, the circumferential pitches of lateral grooves are varied so as to change pulse noises generated from the lateral grooves to so called "white noise". As a result, the circumferential lengths of the resultant blocks between the lateral grooves are varied, and relatively long blocks are formed.
However, when long blocks are formed, lateral drainage at those portions is hindered, and water is liable to remain undischarged, which deteriorates the wet performance. To promote discharge, the width of the main groove (wide circumferential groove) can be increased, but due to resonance of the main groove high-frequency, noise increases, which deteriorates the low noise performance.